Did you turn an existing garage into habitable space? Carpet tiles directly on concrete?

If you have a utility sink in the garage, perhaps the trap is dry.

Millworkman - Carpet tiles were placed directly on concrete. Could that create an odor?

dr saj - no sink in the garage or plumbing of any kind. Gutter is clean too.

Joseph Corlett - hmm but I’m not sure where the dead animal would be. I can’t see any spots in any walling they could have gotten into and the roof is all good.

I’m guessing carpet tiles.

General geographic area where you are located...Arizona desert...Houston...Florida?

Because moisture could be leaching through the slab. Lift some tiles and check for moisture/ mold....

Moisture was able to dissipate and evaporate thru the concrete. Your carpet tiles probably have a vinyl backing which is now trapping the moisture and creating a mold sandwich. Pure speculation but a thought none the less. Not all garage slabs are prepared to be used as is in a habitable space as most have no waterproofing or vapor barrier below the slab so the moisture has to go somewhere.

Millworkman - thanks for the responses! Judging by the patch job outside the garage it seems there is likely no vapor barrier. The carpet tiles have a rubber backing. we actually rent the space (landlord is unhelpful which is why I’d have to prove if there is an issue). Is it possible the odor would be less pungent on the concrete itself and more pungent in the air? Here’s a photo of before we moved in (they added the tiles)

Ci_lantro - out in Southern California. Overall very dry weather but I do imagine there is no vapor barrier since it looks like this on the outside

Any food items stored out there? Any recycling bins or trash cans? We've had garage odors twice...once from a bag of potatoes someone set down as they came in with groceries and then forgot for several weeks. Second time was caused by my kid carrying a leaking garbage bag over the carpeted area of the garage. He told us about the leak, told us he'd cleaned up, didn't mention that he assumed "cleaning up" meant the concrete part of the floor and not the carpeted part.

Oh, and if you have any teenagers or other sportsy people, never discount the amount of stench that can be generated by a pair of shoes or a gym bag tossed into a corner and forgotten.

SapphireStich - nope no food items of any sort in there or dirty clothes! I’ve done a pretty intense cleaning to make sure there was no easy culprit

You may be OK as far as moisture is concerned in SoCal. But that slab is pretty nasty looking--who knows what kind of stink is embedded in the concrete. Old used motor oil, weed killer, garbage can leakage.